In Missouri at least Ed I ran into several churches that had no history of being in a Baptist denomination before becoming Independent Baptists. Now as you've said, that just could be my personal experience. But when I'd ask them why they were Baptists the only answer I would get is that they baptize by immersion. Maybe I just ran into the quirky churches. But there are a lot of little independent Baptist churches both in Missouri and parts of Indiana I'd been in. Two of them were in Rushville, IN. There was one ABC church one SBC church and two independent churches. One quite clearly said that they were "Fundamentalist Baptist, Pre-Millennial and KJV Only" right on the church sign.
At least there was no false advertising.
Again they had no discernible connection to a previous Baptist organization that I ever heard about.